Synthetic rutile process a

ABSTRACT

A process for recovering titanium as synthetic rutile from an ilmenite unsuited to the standard Becher process by treating the ilmenite in a reducing atmosphere in the presence of a carbonaceous reductant to yield reduced ilmenite in which iron oxides in the ilmenite have been reduced to metallic iron, and separating the metallic iron to obtain a synthetic rutile product. The ilmenite is treated at an elevated temperature lower than that for which the TiO 2  content of the synthetic rutile product is highest but at which there is substantially no reoxidation of metallic iron. The carbonaceous reductant comprises coal selected for a gasification reactivity that increases the rate of reduction of iron oxides and titanium species that at least partly offsets the lowered TiO 2  content of synthetic rutile product resulting from the lower elevated temperature, and achieves a TiO 2  content of ≧90% in the synthetic rutile product.

FIELD OF THE INVENTION

This invention relates to the recovery of titanium as synthetic rutilefrom titaniferous ores, and in particular from primary ilmenites, hybridilmenites and other ilmenites with a relatively high proportion of ironor problem impurities or a relatively low proportion of titanium.

BACKGROUND OF THE INVENTION

The standard process by which titanium dioxide is recovered from theilmenite component of Western Australian mineral sands deposits is theBecher reduction process in which the ilmenite is roasted in a rotarykiln in the presence of coal and a reducing atmosphere so as to reduceiron oxides in the ilmenite to metallic iron, which is then separated byaqueous oxidation to obtain a product known as synthetic rutile,typically having a TiO₂ content of 90% or greater. The synthetic rutileis a feedstock for further processing to white paint pigment and otherapplications. These further processes are sensitive to a minimum TiO₂content, and the output of the Becher process is in turn dependent on arelatively tight ilmenite feed specification, e.g. in Western Australiaan iron content measured as FeO<12%. In practical terms this limits thefeedstock for the Becher process to secondary ilmenites, also known asaltered or weathered ilmenites.

Primary ilmenites, which have a higher iron content, are not suitablefor the Becher process but in Western Australia for 16%<FeO<24%so-called sulphate ilmenites have commercial value as a feedstock forthe alternative sulphate process route to TiO₂. Between the Becher andsulphate ranges, i.e. 12%<FeO<16%, ilmenites, known in this range ashybrid ilmenites, have no commercial use.

The strict upper limit on FeO content for Becher process ilmenitefeedstock relates to the prevention of iron reoxidation duringreduction. Circumstances that give rise to reoxidation in the kiln aredifficult to measure and control but it is known that reoxidation ismore significant with primary ilmenite due to its higher iron contentand the resultant risk of agglomeration or sintering and boulderformation. It is known that susceptibility to reoxidation (and thereforeto the formation of agglomerates) can be countered by lowering the kilnoperating temperature: for example lowering the temperature from around1100 to 1150° C., a typical Becher process range, to the vicinity of1000-1025° C. can reduce agglomerate/sinter formation to acceptablelevels. The problem is that the resultant rate of synthetic rutileproduction is uneconomic.

The restrictive ilmenite specification for the Becher process isbecoming a more urgent problem in locations where secondary ilmeniteresources are diminishing. From the perspective of the owners of theseresources, it has been and remains desirable to extract greatercommercial returns for the resource, from both the hybrid and sulphateranges of FeO content.

In other ilmenite provinces, e.g. the Murray Basin of Victoria and NewSouth. Wales, the available ilmenite is not suitable as Becher processfeedstock because of a high content of disadvantageous impurities,notably magnesium and chromium, and a consequent lower proportion oftitanium. For example, the standard feed specification for WesternAustralia secondary ilmenite to the Becher process is FeO<12%,57%<TiO₂<65%. Murray Basin ilmenites typically have a TiO₂ contentaround 54-56%, with Mg typically present in the range 1.5 to 2.5% and Craround 1%.

It is accordingly an object of this invention to provide a commerciallyuseful process for recovering titanium dioxide values from primaryilmenites, hybrid ilmenites and other ilmenites with a relatively highproportion of iron or problem impurities or a relatively low proportionof titanium. These ilmenites are collectively referred to herein asilmenites unsuited to the standard Becher process.

Reference to any prior art in the specification is not, and should notbe taken as, an acknowledgment or any form of suggestion that this priorart forms part of the common general knowledge in Australia or any otherjurisdiction or that this prior art could reasonably be expected to beascertained, understood and regarded as relevant by a person skilled inthe art.

SUMMARY OF THE INVENTION

For primary ilmenites, FeO>16%, it has been found that the rate ofsinter formation through reoxidation at 1100° C. may be as high as sixtimes that for ilmenite of FeO<12%, and that this can only be preventedby substantially lowering the temperature of the reducing treatmentbelow that normally employed for the Becher process. It has been furtherfound that synthetic rutile of an acceptable grade, >93%, can still beproduced at temperatures such as 1025° C., but the rate of production ofsynthetic rutile is unacceptably low. In accordance with the invention,it has been surprisingly found that this unacceptable outcome renderingthe use of primary or hybrid ilmenites uneconomic for the Becher processcan be offset and indeed overcome by the employment of a coal reductanthaving a gasification reactivity that results in an increased rate ofreduction of iron oxides and titanium species.

The invention provides a process for recovering titanium as syntheticrutile from an ilmenite unsuited to the standard Becher process,including the steps of treating the ilmenite unsuited to the standardBecher process in a reducing atmosphere in the presence of acarbonaceous reductant whereby to convert the ilmenite to reducedilmenite in which iron oxides in the ilmenite have been reduced tometallic iron, and separating out the metallic iron so as to obtain asynthetic rutile product. The process is characterised in that theaforesaid treatment of the ilmenite is at an elevated temperature lowerthan that for which the TiO₂ content of the synthetic rutile product ishighest but at which there is substantially no reoxidation of themetallic iron, and in that the carbonaceous reductant comprises coalselected for a gasification reactivity that results in an increased rateof reduction of iron oxides and titanium species effective to at leastpartly offset the lowered TiO₂ content of the synthetic rutile productresulting from said lower elevated temperature, and to achieve a TiO₂content of 90% or greater, preferably at least 93%, in the syntheticrutile product.

It may be that the gasification reactivity of the coal is simplysufficiently high to achieve said offset, but a high value for thegasification reactivity may not be sufficient. It may be relatively highas a coal gasification reactivity, by which is meant in the context ofthis specification significantly higher than the average of all coals.In practical terms, this means that the gasification reactivity istowards the higher end of the range of gasification reactivity generallyfound in coals. The gasification reactivity is preferably greater than0.005 g-g/min at 850° C., more preferably greater than 0.01 g-g/min at850° C., both values for coal char at atmospheric pressure.Alternatively or additionally the gasification reactivity is preferablyat least twice that of typical Collie coal, more preferably at leastthree times that of typical Collie coal.

The elevated temperature of said treatment is preferably less than 1050°C., more preferably between 975 and 1035° C., and most preferably in therange 1000 to 1030° C.

One known indicator of higher coal gasification reactivity is the levelof ion-exchanged calcium, although it is thought that other impurityelements can play a similar role. The selected coal accordinglypreferably has impurity levels of ion-exchanged inorganic elementssufficiently high to increase the gasification rate of the coal thusimproving the reducing conditions in the process and thereby increasingthe rate of reduction of iron oxides and titanium species. Such elementsmay include alkaline earth elements such as calcium and magnesium, oralkali elements such as sodium, or iron. Coal containing relatively highlevels of ion-exchanged calcium has been found to be particularlyuseful.

A measure of sufficiently high levels of ion-exchanged inorganicelements is the acid extractable proportion of the elements: this isdesirably greater than 50%, more preferably greater than 70%, mostpreferably greater than 80%. Usefully, at least one such inorganicelement is present to the extent of at least 0.2% db on a dry coalbasis.

While the coal may be of any rank including bituminous, a suitable coalcomprises a sub-bituminous or lignite coal selected for a total moisturecontent between 5 and 40%, or an inherent moisture content in the range5 to 25%, in the latter case most preferably about 20% or less.Volatiles content is preferably greater than 30%, most preferablygreater than 40%. Ash content is preferably below 10%, most preferablybelow 5%.

Ultimate hydrogen content of the coal, on a dry ash basis, is preferablygreater than 4%. Ultimate carbon content is preferably greater than 65%.Ash fusion temperature may be above 1100° C., on an initial deformationtemperature (I.D.T.) basis, above 1200° C. on a hemisphericaltemperature (H.T.) basis (more preferably at least 1150° C. and 1250° C.respectively).

Preferably, char is mixed with the ilmenite before it is delivered forthe aforesaid treatment step. The presence of char mixed with theilmenite has been found to further assist in reducing the rate ofagglomeration or sintering arising from reoxidation.

Preferably, the sulphur content of the coal is less than 1% w/w, morepreferably less than 0.5%, most preferably less than 0.2%. Preferably,there is no additional sulphur present for most of the duration of saidtreatment. It has been found that sulphur contained in the coal abovethese preferred levels (for example by providing a blend of low-sulphurand high sulphur coal fractions) or present by virtue of additionalsulphur, adversely affects the reactivity of the ilmenite, i.e. the rateof metallisation (the speed at which iron oxide is converted to metalliciron in the reduction treatment step).

Thus, if in order to further increase the TiO₂ content of the syntheticrutile product of the process, it is desired to deliver sulphur to theilmenite during said treatment step, e.g. for removing manganeseimpurity as manganese sulphide, such delivery is effected only laterduring the duration of the reduction treatment, for example only duringthe last 3 hours of a 9 hour treatment.

The iron content of the ilmenite, expressed as FeO, may be in the rangeFeO>12%, for example in the range 12%<FeO<30%.

Preferably, free oxygen in the treatment atmosphere is no greater than2.5% and preferably less than 2%, most preferably less than 1%.

Preferably, the treatment at elevated temperature in a reducingatmosphere is carried out in an inclined rotary kiln of the kindnormally employed for the Becher process. The material recovered fromthe lower end of the kiln is known as reduced ilmenite, a mix ofmetallic iron and titanium dioxide with a residual content of iron andother impurities. This reduced ilmenite is cooled to prevent reoxidationof metallic iron and then passed to the separation step.

The iron removal step may be any suitable separation method employed inBecher reduction processes. A typical such method is an aqueousoxidation step in which the metallic iron is oxidised or rusted tomagnetite, haematite or lepidocrocite in a dilute aqueous solution ofammonium chloride catalyst.

A final stage to remove further iron and manganese impurities may entailan acid leach or wash, typically employing sulphuric acid (e.g. 1 to2M—at least double the strength in the standard process).

It will be appreciated that the process of the invention is applicableto primary and hybrid ilmenites (however locally defined) and to otherilmenites unsuited to the standard Becher process, e.g. Murray Basinilmenites of relatively low Ti content (e.g. 54-56%) and higher impuritycontent (notably Mg 1.5-2.5%, Cr 1%).

EXAMPLES

A sequence of tests was carried out employing simple bulk samples of anumber of primary ilmenites selected to have a range of FeO contents.These ilmenites were Yoganup Extended, Wagerup, Cloverdale and Waroonailmenites from different resources in Western Australia. YoganupExtended ilmenite was chosen for its high (27%) FeO content, which wouldrepresent a worst case scenario in sintering and reduction test results.The other three ilmenites have FeO contents within the afore-mentionedsulphate ilmenite range.

To initially test the effect of temperature, two large samples ofYoganup Extended primary ilmenite and a secondary standard Capelilmenite (FeO 12%) were reduced using Collie coal at the standard 1100°reduction temperature. Table 1 sets out an assays for each of the fiveselected ilmenites. Analysis of the ilmenite and reduced ilmenite(RI—the product of the treatment prior to separation of the metalliciron) showed minimal sintering in the primary ilmenite during theinitial reduction.

To establish the temperature effect on sintering, the RI samples weresubjected to various temperatures and oxygen concentrations whilst beingheld in a furnace. RI samples were placed on a platinum crucible andexposed to mixtures of oxygen and nitrogen of 1.2% O₂, 2.46% O₂ and 5.3%O₂. Tests were conducted at 1000, 1050, 1100 and 1150° C. Sinterproduction was measured by sizing the original RI and the productremoved from the platinum boat after 1 minute. Screening was initiallyconducted using 10 standard aperture sizing betweens 106 um and 1 mm.Analysis of the sizing results showed the best measure of sintering tobe the increase in the amount of +250 um and +1 mm material. For thisreason in later tests screening was carried out with only 250 um and 1mm screens.

The presence of char also has an effect on sintering due to theprotection it offers from reoxidation. Since the kiln may have zones ofsegregation of coal and RI it was decided to test the degree ofsintering in the both the presence and absence of char.

The reference feed ilmenite was a 14% FeO sample selected to form thebasis of comparison. The reference ilmenite represents the highest FeOlevel that had been processed through nearby SR kilns without incident.Results from the reference ilmenite set a benchmark for the maximumacceptable level of sintering and by how much reduction temperaturesneed to be dropped to achieve the same sintering levels.

Table 2 shows the degree of sintering at 1000, 1050, 1100 and 1150° C.after 1 minute of exposure to a 5.3% oxygen/nitrogen mixture. Sizings ofRI and ilmenite are also shown for reference.

The data from Table 2 is also plotted in FIG. 1. The followingobservations can be made regarding increased temperature in the presenceof surplus oxygen:

-   -   The degree of sintering increases with higher temperatures. This        is evident by a reduction in the amount of fine grained material        in the 125 and 150 um size range. The amount of agglomerates in        the 212 and 250 um size range more than doubles as temperature        increases. There is also a sharp increase in the amount of +1 mm        sized material which represent multi-particle agglomerates        compared to 2-particle agglomerates.    -   The degree of agglomeration of +1 mm primary (Yoganup Extended)        ilmenite (FIG. 2, Table 3) compared to standard Capel ilmenite        was measured to be 6 times. At 1150° C. the amount of +1 mm        sinter was 9.9% in Capel ilmenite and 67% in the primary        ilmenite.    -   At 1000° C. the degree of sintering in both Capel ilmenite and        primary ilmenite was negligible. The degree of sintering        increased proportionately with temperature and time. When the        exposure time was left longer than 1 minute the entire sample        was found to fuse into a single lump.

Plotting the amount of +250 um in RI against temperature showed a pointof inflection at around 1050° C. At temperatures above 1000° C. the risein sintering rates was significant particularly at higher oxygenconcentrations of 5.3%. However in most practical instances an oxygenconcentration of 1 to 2% is the most likely scenario except in theinstance of a cracked shell air tube. At lower oxygen concentrations ofaround 1% to 2% the amount of +250 um sinter began to increase at around1020° C.

FIG. 3 shows the amount of plus +250 um sinter formed after one minuteat increasing oxygen concentrations for different reductiontemperatures. It will be seen that there is a marked rate of diminutionat temperatures below 1100° C. for an oxygen concentration below 2.5%.

Having established that agglomeration and sintering could be minimisedif the kiln temperature was in the region of 1000 to 1025° C., reductiontests were carried out respectively employing Collie coal, commonly usedin Western Australia as the solid reductant in commercial operations ofthe standard Becher process using secondary or altered ilmenites, and acoal determined by testwork to have a high gasification reactivity. Thisreactive coal was found to have a gasification reactivity about fivetimes higher than the Collie coal. A consequence is that the generationof reduction gases (CO,H₂ etc) will occur at lower temperatures than forCollie coal and it was thus thought possible that ilmenite reductionwould also occur at lower temperatures, thereby allowing the option ofreducing kiln operational temperatures to the desired level.

The gasification (CO₂) reactivity behaviour of char samples (200-300 μm)produced from the reactive coal and the Collie coal was determined usinga high-pressure thermogravimetric analyser. For samples of about 300 mg,CO₂ reactivity was determined from the rate of sample mass loss due tothe reaction C+CO₂ (g)

2CO(g). Tests were performed under two temperature conditions atatmospheric pressure: isothermal at 850° C. and a varying temperatureincreased from 700° C. at a rate of 2° C./min. The latter test allowedthe temperature dependence of the gasification reaction to bedetermined.

The relative reactivities of the coal chars are presented in Table 4. Itwill be seen that, as noted above, the reactive coal was found to have agasification reactivity at 850° C. about five times higher than theCollie coal.

Elemental analyses of the coals is set out in Table 5. It will be seenthat the reactive coal has materially higher levels of calcium andmagnesium (a full order of magnitude difference) relative to the Colliecoal and this was found to be the case also in analyses of therespective ash residues. On a dry coal basis, each is about 0.2% db. Itwas established that the calcium and magnesium, and also the iron, werepresent in an ion-exchanged form in the reactive coal. This wasestablished by demonstrating that the acid extractable levels of Ca, Mgand Fe in the reactive coal were of the order of 85-95%, while theCollie coal had much lower levels (less than 50%) of acid extractableCa, Mg and Fe. The presence of ion-exchanged calcium, iron, sodium and,to a lesser extent magnesium, in coals has been found to enhance thegasification reactivity. By increasing the gasification rate of thecoal, the reducing conditions in the process are improved, therebyincreasing the rate of reduction of iron oxides.

Each ilmenite was reduced at 1025° C., which has been found to be themaximum desirable operating temperature from previous sintering tests.Samples were extracted from the reduction pot at 4.5, 5.0, 5.6, 6.2,6.8, 7.4 and 9.0 hrs. Titrations were carried out on each sample todetermine the amount of metallic iron formed. The metallisation rate foreach ilmenite sample is shown in Table 6.

Table 6 clearly shows the slower reduction rates of Collie coal comparedto the reactive coal, taking nearly the full 9 hours to achieve 95%metallisation compared to the reactive coal taking just over 5.6 hours.Cloverdale ilmenite reduced significantly faster than either of theother three sulphate ilmenites with a behaviour more similar to analtered secondary ilmenite. Complete reduction was achieved in just over5.6 hrs. Cloverdale ilmenite also has the lowest FeO content of 18.4%and lowest MnO level of 0.96%.

Expected kiln throughput rates for the different sulphate ilmenites areshown in Table 7. The baseline reduction shows Yoganup Extended sulphateilmenite (27% FeO) with Collie coal at 22.1 t/hr which is an approximate45% reduction in capacity compared to typical throughputs. All reductiontemperatures are assumed as 1025° C. to minimise the likelihood ofsintering.

In contrast, throughput rates of 31.8 t/hr (20% reduction) are expectedfor Yoganup extended sulphate ilmenite using the reactive coal at 1025°C., and throughput rates of 69.9 t/hr (75% increase) are expected forCloverdale sulphate ilmenite using the reactive coal at 1025° C.

The expected feed rates as shown in Table 7 are depicted graphically inFIG. 4 to show that two sulphate ilmenites performing above currenttypical feed rates and two below. The two best performing sulphateilmenites had the lowest FeO of 18.4% (Cloverdale) and 19.1% (Waroona).The lowest performing sulphate ilmenites (>20% reduction in throughput)had FeO levels of 27% (Yoganup Extended) and 19.7% (Wagerup).

RI samples from the reduction of sulphate ilmenite were acid leachedusing a 2M sulphuric acid concentration to produce a simulated syntheticrutile (SR). From previous leach tests on Yoganup. Extended primaryilmenite a 2M acid concentration was found to produce the optimum SRTiO₂ grade. The 2M strength is approximately twice the normal strengthneeded with altered ilmenites (0.5 to 1.0M) required to fully extractall of the iron.

Table 8 sets out the assays of the resultant synthetic rutile products.Acceptable SR TiO₂ grades were obtained from 3 of the 4 sulphateilmenite samples tested using the reactive coal at 1025° C. UnacceptableSR TiO₂ grades (<90% TiO₂) from Collie Coal (89.61%) occurred due to theslower metallisation rates and incomplete metallisation at the end of 9hours at 1025° C. 93.3% TiO₂ grade was achieved at 1100° C. due tohigher metallisation rates, however the higher reduction temperaturesalso has a much higher risk of sintering.

Acceptable SR TiO₂ grades (>93%) were produced from Cloverdale (95.12%)and Yoganup Extended (93.00%) primary ilmenite at 1025° C. using thereactive coal. Acceptable but below specification SR grades (92.08%)were produced from Waroona sulphate ilmenite at 1025° C. using thereactive coal.

Unacceptable SR TiO₂ grades (88.67%) were produced from Wagerup sulphateilmenite, which was also the slowest reducing of the four sulphateilmenites. A lower overall total metallisation completion of 96.6%(Table 6) compared to 98% resulted in a residual SR iron level of 8.76%.

FIG. 5 illustrates the rates of reduction of iron oxides (as measured bymetallic iron formation) and titanium species, for respective kilnreductions of a primary ilmenite under similar conditions with Colliecoal and the reactive coal. An assay of the primary ilmenite employed isprovided under the graphs.

As used herein, except where the context requires otherwise, the term“comprise” and variations of the term, such as “comprising”, “comprises”and “comprised”, are not intended to exclude further additives,components, integers or steps.

It will be understood that the invention disclosed and defined in thisspecification extends to all alternative combinations of two or more ofthe individual features mentioned or evident from the text or drawings.All of these different combinations constitute various alternativeaspects of the invention.

TABLE 1 Ilmenite assays Standard Yoganup Wagerup Cloverdale WaroonaCapel % Ext. % % % % FeO 14.0 27.0 19.7 18.4 19.1 TiO₂ 57.5 53.0 52.354.8 53.9 Fe₂O₃ 38.9 46.4 48.0 42.2 43.1 SiO₂ 0.90 0.05 0.14 0.41 0.48ZrO₂ 0.11 0.03 0.04 0.05 0.05 P₂O₅ 0.05 0.02 0.00 0.03 0.01 Al₂O₃ 0.620.34 0.35 0.51 0.77 Nb₂O₅ 0.16 0.13 0.10 0.16 0.12 Cr₂O₃ 0.04 0.0300.030 0.037 0.038 MgO 0.22 0.19 0.17 0.06 0.07 CaO <0.001 <0.001 <0.0010.000 0.000 V₂O₅ 0.18 0.15 0.15 0.19 0.19 MnO 1.30 1.68 1.80 0.96 1.61 S0.02 <0.005 0.007 0.000 0.000 Th 103 51 119 43 135 (ppm) U 11 10 6 0 0(ppm)

TABLE 2 Sinter fractions formed in Yoganup RI heated at 1000, 1050, 1100and 1150° C. with oxygen concentrations of 5.3% O₂. 1000 C. 1050 C. 1100C. 1150 C. 1 min 1 min 1 min 1 min Reduced yog. Ext. Size 5.3% O2 5.3%O2 5.3% O2 5.3% O2 ilmenite ilmenite Fraction % % % % % % +1 mm 7.7 12.28.7 12.3 0 0 −1 mm + 710 0.1 0.1 0.5 1.6 0 0 −710 + 500 0.5 0.2 2.4 3.30 0 −500 + 355 2.5 0.2 5.3 6.1 0.3 0.05 −355 + 250 2.2 3 8.4 9.7 1.1 0.9−250 + 212 5.2 8.6 7.7 11.3 2.9 3 −212 + 180 9 11.7 13.2 11.8 11.5 12.3−180 + 150 23.5 20.5 18.7 16.9 31.5 27 −150 + 125 30.7 26.7 22.2 17.232.1 34.4 −125 + 106 10.9 10.9 8.2 6.2 12.3 13.8 −106 7.7 6 4.8 3.6 8.38.4 d50 151 159 174 197 148 145 AFS 116 110 103 94 125 127

TABLE 3 Sinter produced by the oxidation of Ilmenite in a platinum boatfor 1 minute at 2.46 vol % O₂ Temperature Standard Ilm Yoganup Ext. DegC. +250 um +1 mm +250 um +1 mm 1150 45.9 9.9 80.7 67.0 1100 38.6 7.773.8 57.2 1050 21.4 5.0 51.9 32.3 1000 15.3 1.7 19.4 6.3

TABLE 4 Char-CO₂ Gasification Reactivity Char CO₂ Reactivity g-Activation Sample Description g/min @ 850° C. Energy kJ/mol Char fromReactive Coal 0.0113 226.7 Char from Collie Coal 0.00205 187.0

TABLE 5 Elemental Analysis (% dry coal basis) Collie Coal Reactive Coal% db % db Carbon 71.4 68.5 Hydrogen 4.1 4.9 Nitrogen 1.3 0.84 S_(total)0.54 0.11 Cl_(total) 0.01 0.00 Si 1.06 0.34 Al 0.88 0.17 Fe 0.34 0.38 Ti0.086 0.014 K 0.031 0.02 Mg 0.02 0.22 Na 0.02 0.01 Ca 0.05 0.56

TABLE 6 Metallisation rates of Yoganup Extended, Wagerup, Cloverdale andWaroona sulphate ilmenite Metallisation (%) Yogi Ext Yogi Ext WagerupCloverdale Waroona Collie Reactive Reactive Reactive Reactive Time (hrs)Coal Temp coal coal coal coal coal 4.5 951 21.23% 17.52% 31.06% 29.99%5.0 989 31.22% 53.63% 42.47% 87.46% 74.25% 5.6 1025 45.80% 94.11% 93.00%94.26% 93.73% 6.2 1025 63.08% 93.71% 94.24% 96.33% 97.07% 6.8 102578.32% 96.33% 95.35% 97.34% 98.83% 7.4 1025 89.18% 97.03% 96.38% 97.79%97.74% 9.0 1025 97.48% 98.02% 96.62% 98.77% 98.13%

TABLE 7 Expected kiln feed rates (at 1025° C.) from Yoganup Extended,Wagerup, Cloverdale and Waroona Sulphate Ilmenites reduced with theReactive Coal Reducibility Kiln Kiln Log Ilmenite Bed Gas Feed ConstantFeT FeO Temp Temp Rate Yoganup Ext + 20.42 32.4 27.04 1025 1067 22.1Collie coal Yoganup Ext + 21.28 32.4 27.04 1025 1095 31.8 Reactive coalWagerup + 21.17 33.5 19.66 1025 1091 30.5 Reactive coal Cloverdale +23.50 29.5 18.40 1025 1219 69.9 Reactive coal Waroona + 21.98 30.2 19.111025 1129 42.2 Reactive coal

TABLE 8 SR grades produced following reduction of Yoganup Extended,Wagerup, Cloverdale and Waroona Sulphate Ilmenites reduced with ReactiveCoal COAL Collie Reactive Reactive Reactive Reactive Redn Temp 1025 10251025 1025 1025 Leach Strength 2M 2M 2M 2M 2M Ilmenite Yog Ext. Yogi Ext.Wagerup Waroona Cloverdale Ilmenite FeO 27.0% FeO 27.0% FeO 19.7% FeO19.1% FeO 18.4% FeO Ilmenite TiO2 53.0% TiO2 53.0% TiO2 52.3% TiO2 53.9%TiO2 54.8% TiO2 Ilmenite MnO 1.68% MnO 1.68% MnO 1.80% MnO 1.61% MnO0.96% MnO TiO2 89.61 93.00 88.67 92.08 95.12 Fe2O3 6.55 4.65 8.76 4.171.70 SiO2 0.38 0.37 0.41 0.64 0.54 ZrO2 0.05 0.06 0.06 0.06 0.05 P2O50.01 0.01 0.01 0.01 0.01 Al2O3 0.63 0.66 0.54 1.09 0.63 Nb2O5 0.22 0.230.18 0.20 0.28 Cr2O3 0.09 0.07 0.07 0.07 0.07 MgO 0.40 0.42 0.36 0.350.35 CaO <DL 0.01 0.01 0.01 0.02 V2O5 0.23 0.24 0.24 0.25 0.26 MnO 2.332.70 2.74 2.59 1.54 S 0.02 0.005 <DL <DL <DL Th (ppm) 50 48 134 111 21 U(ppm) <DL 10 11 13 20

1. A process for recovering titanium as synthetic rutile from an ilmenite unsuited to the standard Becher process, including the steps of treating the ilmenite unsuited to the standard Becher process in a reducing atmosphere in the presence of a carbonaceous reductant whereby to convert the ilmenite to reduced ilmenite in which iron oxides in the ilmenite have been reduced to metallic iron, and separating out the metallic iron so as to obtain a synthetic rutile product, wherein said treatment of the ilmenite is at an elevated temperature lower than that for which the TiO₂ content of the synthetic ruffle product is highest but at which there is substantially no reoxidation of the metallic iron, and wherein the carbonaceous reductant comprises coal selected for a gasification reactivity that results in an increased rate of reduction of iron oxides and titanium species effective to at least partly offset the lowered TiO₂ content of the synthetic rutile product resulting from said lower elevated temperature, and to achieve a TiO₂ content of 90% or greater in said synthetic rutile product.
 2. A process according to claim 1 wherein the elevated temperature of said treatment is less than 1050° C.
 3. A process according to claim 2 wherein the gasification reactivity is sufficiently high to achieve said offset.
 4. A process according to claim 3 wherein said gasification reactivity of the coal is relatively high (as defined herein).
 5. A process according to claim 1 wherein the selected coal has impurity levels of one or more ion-exchanged inorganic elements sufficiently high to increase the gasification rate of the coal thus improving the reducing conditions in the process and thereby increasing said rate of reduction of iron oxides and titanium species.
 6. A process according to claim 5 wherein the acid extractable portion of said one or more ion-exchanged inorganic elements is at least 50%.
 7. A process according to claim 1 wherein the selected coal has relatively high impurity levels of ion-exchanged calcium.
 8. A process according to claim 1 wherein the selected coal is a sub-bituminous or lignite coal.
 9. A process according to claim 8 wherein the selected coal has a total moisture content between 5 and 40%, volatiles content greater than 30%, and ash content below 10%.
 10. A process according to claim 8 wherein inherent moisture content of the selected coal is 20% or less, volatiles content is >40% and ash content is <5%.
 11. A process according to claim 1 further including mixing char with the ilmenite before it is delivered for said treatment step.
 12. A process according to claim 1 wherein the sulphur content of the coal is less than 1% w/w, and there is no added sulphur present for most of the duration of said treatment.
 13. A process according to claim 12, wherein the sulphur content of the coal is less than 0.5%.
 14. A process according to claim 12, wherein the sulphur content of the coal is less than 0.2%.
 15. A process according to claim 12 further including delivering sulphur to the ilmenite during said treatment step for removing manganese impurity as manganese sulphide, such delivery being effected only later during the duration of the reduction treatment.
 16. A process according to claim 1 wherein the iron content of the ilmenite, expressed as FeO, is greater than 12%.
 17. A process according to claim 16 wherein the iron content of the ilmenite, expressed as FeO, is less than 30%.
 18. A process according to claim 1 wherein free oxygen in the treatment atmosphere is no greater than 2.5%.
 19. A process according to claim 1 wherein the Ti02 content achieved in said synthetic rutile product is at least 93%.
 20. A process according to claim 1 wherein the ilmenite unsuited to the standard Becher process is one of a primary ilmenite and a hybrid ilmenite.
 21. A process according to claim 1 wherein the ilmenite unsuited to the standard Becher process is a Murray Basin ilmenite of relatively low Ti content and higher impurity content.
 22. A process according to claim 3 wherein the selected coal has impurity levels of one or more ion-exchanged inorganic elements sufficiently high to increase the gasification rate of the coal thus improving the reducing conditions in the process and thereby increasing said rate of reduction of iron oxides and titanium species.
 23. A process according to claim 22 wherein the acid extractable portion of said one or more ion-exchanged inorganic elements is at least 50%.
 24. A process according to claim 3 wherein the selected coal has relatively high impurity levels of ion-exchanged calcium.
 25. A process according to claim 3 wherein the selected coal is a sub-bituminous or lignite coal.
 26. A process according to claim 25 wherein the selected coal has a total moisture content between 5 and 40%, volatiles content greater than 30%, and ash content below 10%.
 27. A process according to claim 25 wherein inherent moisture content of the selected coal is 20% or less, volatiles content is >40% and ash content is <5%.
 28. A process according to claim 5 wherein the selected coal is a sub-bituminous or lignite coal.
 29. A process according to claim 28 wherein the selected coal has a total moisture content between 5 and 40%, volatiles content greater than 30%, and ash content below 10%.
 30. A process according to claim 28 wherein inherent moisture content of the selected coal is 20% or less, volatiles content is >40% and ash content is <5%.
 31. A process according to claim 28 wherein the acid extractable portion of said one or more ion-exchanged inorganic elements is at least 50%.
 32. A process according to claim 3 wherein the sulphur content of the coal is less than 1% w/w, and there is no added sulphur present for most of the duration of said treatment.
 33. A process according to claim 32, wherein the sulphur content of the coal is less than 0.5%.
 34. A process according to claim 32 further including delivering sulphur to the ilmenite during said treatment step for removing manganese impurity as manganese sulphide, such delivery being effected only later during the duration of the reduction treatment.
 35. A process according to claim 1 wherein the iron content of the ilmenite, expressed as FeO, is less than 30%.
 36. A process according to claim 3 wherein the Ti02 content achieved in said synthetic rutile product is at least 93%.
 37. A process according to claim 3 wherein the ilmenite unsuited to the standard Becher process is one of a primary ilmenite and a hybrid ilmenite.
 38. A process according to claim 3 wherein the ilmenite unsuited to the standard Becher process is a Murray Basin ilmenite of relatively low Ti content and higher impurity content.
 39. A process according to claim 12 wherein the Ti02 content achieved in said synthetic rutile product is at least 93%.
 40. A process according to claim 12 wherein the ilmenite unsuited to the standard Becher process is one of a primary ilmenite and a hybrid ilmenite.
 41. A process according to claim 12 wherein the ilmenite unsuited to the standard Becher process is a Murray Basin ilmenite of relatively low Ti content and higher impurity content. 